Given that several PDE4 inhibitors approved for various medical conditions, including chronic obstructive pulmonary disease and asthma [13], potentially inhibiting all splice products of the four PDE4 genes, which may confer cardiovascular risks, it is necessary to further delineate the effect of PDE4 isoforms in HF to develop isoform-specific PDE4 inhibitors. Here, PDE4A is linked to hydrops fetalis.